INTRODUCTION

Seismic‐hazard analyses and stress tests for critical infrastructures show limitations in the treatment of extreme events. These extreme events can be great earthquakes and/or their cascading effects, generally not foreseen in risk analysis and management (e.g., Komendantova et al., 2014). For instance, earthquake ruptures are known to potentially propagate over several segments (e.g., Eberhart‐Phillips et al., 2003; Fliss et al., 2005), yet fault segments are still modeled as individual faults in most regional seismic‐hazard models based on expert opinion and on limited paleoseismic data. Rate anomalies (known as the bulge) in the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF2) are in part due to the neglect of possible links between fault segments (Field et al., 2009). Recent catastrophes, such as the 2011 Mw 9.0 Tohoku earthquake and its consequences (e.g., Norio et al., 2011), have demonstrated the need for “a targeted reassessment of the safety margins” of critical infrastructures (European Nuclear Safety Regulators Group [ENSREG], 2011).

The present study is designed to address the issue of potentially unforeseen great earthquakes (1) by proposing criteria for earthquake rupture cascading over fault segments based on geometrical and physical considerations and (2) by assessing the maximum magnitude (Mmax) of these ruptures spanning hundreds of kilometers. Focus is on strike‐slip mechanisms. Different definitions of Mmax have been proposed based on the assumption that no earthquake is expected above that threshold, such as the maximum observed magnitude, the deterministic “maximum credible” magnitude (Reiter, 1990), and the statistical “maximum possible” magnitude (Kijko and Singh, 2011). The predictive power of the statistical approach has been recently shown to be rather poor (Zöller et al., 2013). Furthermore, Holschneider et al. (2014) found it is essentially impossible to infer Mmax from earthquake catalogs alone. Our method to assess Mmax is directly related to the …